Glow tube pulse amplifier



Jan- 15, 1952 c. R.`wu lAMs Erm. 2,582,367

GLOW TUBE PULSE AMPLIFIER Filed June 3. 195o Fr our/Ur J6 I4 A /l f,4A/006 Var/10a' *Wr-L0 0073907' VOLT/466 y,

Patented Jan. 15, 1952 GLOW 'TUBE PULSE AMPLIFIER Charles R. Williams,Hawthorne, and Glenn .Hagen,--Lawndale, Calif., assignors to NorthropAircraft, .1110., Hawthorne, Calif., a corporation ,.of CaliforniaApplication lJune'3, 1950, SeralNo.'1'65,999

4 Claims. l

The present invention relates to pulse amplifiers and more particularlyto a cold cathode glow tube and circuit for Yamplifying pulses such as,for example, may be produced by a radiation ,counter tube exposed togamma radiation.

An object of the invention is to produce asiniple. and effective Apulseamplifier.

It is a Well known property of gas and evapor tubes, ingeneral, that-very lsteep voltage awave fronts and high amplitude current pulsesicanbe obtained from the iii-ing of these tubes while under the stressof a suitable anode to cathode potential. Upon ring, the anode tocathode potential drops rapidly to the burning value characteristic ofthe tube and :high energy-pulses can be derived vfrom the resultantdischarge oi `capacitors connected across'the tube. Usual1y,posi tivevpulses are derived from the cathode .and negative pulses are derivedfrom the anode circuits of such tubes.

Briefly, the present `invention includes the use of a cold cathode glowtube having an anode, a trigger electrode, and a .cold .cathodeenergized by a potential source sulcient to place the opferating point`of the tube on the characteristic voltage-current curve close -to .itsunstable range. A stable glow is established on the cathode and .anegative input pulse isapplied to the trigger electrade, thereby causingthe cathode yglow to .be interrupted, thus allowing the Aanodejpotential to rise. When the anode potentialreaches Athe firing voltageof the tube, the glow is restruck on the cathode. Upon restriking, thesudden potential drop at the anode provides a source of negative pulsessuitable for actuating a counter circuit, for example.

The invention is particularly suited to triggering by a high impedance.pulse source. Forexample, with an input impedance of megohms powergains up to 10,000 can be realized.

The invention will be more fullyunderstood by reference to the followingdescription of the drawings, in which:

Figure 1 is a side view in elevation of one preferred form of coldcathode tube used in the circuit of the present invention.

Figure 2 is a circuit diagram showing the tube of Figure l used as apulse amplifier .according to the present invention.

Figure 3 is a chart showing a typical Voltagecurrent characteristic fora tube such as shown in Figure l.

Figure 4 is adiagram of the input and output `pulse relationship in theYcircuit of vFigure l3.

Figure 5 is a preferred form of pulse amplier usedinaradiation counterdevice.

Figure 6 is a chart showing a typical voltagecurrent characteristic of acrystal diode such as is used in the circuit of Figure 5.

Asshown in Figure 1, the tube preferred for use in the circuits ofFigures 2 and 5 is provided with an envelope l containing an anodewire.2, a cathode wire 3 and a trigger electrode wire 4. These -wirespass through an external pinch 5 to form an anode lead 6 and cathodelead l, and trigger lead S.

A preferred tube is one inch long by 1A; inch in diameter. The gaspressure in the tube, the gas mixture, and the anode to cathode spacingis adjusted to give a desirable ring to burning voltage differential.Electrode spacings of .060 yinch in helium, mixed with 2% water vapor at150 mm. Hg pressure, are satisfactory. Suitable steady state tubecurrents are 0,1 to 0.2 ma. Such a tube will provide a ring to burningdifferential of from to 300 volts and output pulses of similaramplitude.

To accelerate deionization and to promote triggering sensitivity, weprefer that the tube have Vfrom one percent to ve percent of -arecombinable polyatomic gas therein, such as Yhydrogen or water vapor,for example, in addition to the inert gas lling, in accordance with theteachings of acopending Hagen application, Seri-al No. 100,178, filedJune 6, 1949, now Patent No. ,2,575,516 issued November 20, 1951. Theanode, cathode and trigger electrodes may all be simple Wires or rods,and it is preferred that the anode and the cathode be side wires, withthe trigger electrode therebetween.

Referring next to Figure 2 the cathode 3 of tube l is grounded. Thetrigger electrode l is connected to a source of negative pulses throughan input line ril containing an input capacitor i0, the pulse sourcebeing preferably of high .impedance as represented by input resistor il.If the pulse source is of low impedance, a suitable crystal diode or an.oscillation damping resistor, for example, one megohm, may be insertedin 4the input to promote stability.

Anode 2 is connected through a variable anode resistance i2 to thepositive end B+ of a potential source, and is `also connected through acapacitor l5 to an output line I4 which is ground through a shuntrectifying diode t6.

The voltage B+ at the anode 2 is made to be suilicient to cause tube lto strike .quickly to the cathode 3. The current used by the anode 2 is4adjusted by variation of the anode .resistor I 2 to operate at adesirable point on the voltagecurrent curve as typically shown in Figure3. At point a on `this curve, i. e., on the zero slope portion thereof,the tube is stable. At point c on the negative slope, the tube isunstable and will oscillate.' A point such as b can be chosen where thetube is still stable but is highly sensitive to triggering. When at sucha point, the glow discharge at the cathode 3 can be interrupted by thefield produced by a relatively small negative voltage pulse on theadjacent trigger electrode 4.

After cathode current interruption by a negative input pulse, the anodepotential rises, charging capacitor I5 toward the potential of B+; andwhen the firing point is reached, the tube automatically restrikes tothe cathode 3, permitting capacitor I5 to discharge and therebyproviding a negative pulse in the output circuit I4. The relationbetween input, anode and output voltage waveforms is shown in Figure 4;the input pulse voltage curve being there designated as curve I, anodevoltage curve labelled curve A, and the output pulse voltage curvelabelled curve O. When the tube reignites, the anode voltage dropssharply and a negative output pulse is developed across diode I6 by thedischarge of capacitor I5 through the tube. Capacitor I5 and rectifierdiode I6 also act as an anode load to slow the rate of anode voltagerise after triggering, thereby somewhat improving the sensitivity of thecircuit. As is shown in Figure 4, there is a time delay between theinput pulses I and the output pulses O. This delay is proportional toand may be controlled by the size of capacitor I5. Hence, in addition toamplifying, the invention may be used as a delay device.

The tube and circuit of Figure 2 is ideally suited for use as a pulseamplifier between a radiation counter tube, such as a Geiger-Mller tube,and a pulse counter, as shown in Figure 5. A radiation counter tube 20is connected to the trigger electrode 4 of tube I through inputcapacitor I and to voltage source 2i through radiation tube resistor 22.The anode 2 of tube I is connected to source 2| through a fixed anoderesistance 24 and the variable anode resistance I2, which permitsadjustment of the anode voltage to operate the tube at or near point bon the curve of Figure 3.

The output line I4 contains a series output capacitor I5, and the shuntrectifying diode I6, as in the circuit of Figure 2, but4 contains inaddition a second rectifying diode 26 in series with the output. Thislatter rectifier' 26 acts as a buffer to prevent reflection of pulsesback through the output line I4 to the tube I that might causeoscillation thereof.

The output line is then connected to a counter 21 past a shunt loadresistor 28. Counter 21 may be, for example, a ten stage gas tube binarycounter such as has been shown, described and claimed in our copendingapplication, Serial No. 167,572, filed June l2, 1950. Load resistor 28reduces stray pickup on output line I4 that might trigger counter 21.

The tube I is susceptible to triggering by pulses coupled back to theanode 2, such as from a gas tube radiation counter, for example. Figure6 shows the current-voltage characteristic of diode 26 which preferablyis of the germanium crystal type and which has two voltage ranges d andf of conductivity separated by an intermediate range e of highresistivity. When the tube I is triggered, diode 26 is in range f whereit is highly conductive and does not interfere with the charging ofcapacitor I or with the triggering action. When the anode 2 restrikes,the discharging of capacitor I5 forces diode 26 through the highresistance range e into conducting range d which permits a somewhatdiminished pulse to be passed out to the load 21. After the output pulsehas expired, diode 26 falls back into range e through which itprogresses relatively slowly as capacitor I5 is discharging through thenow high resistance of diode 26. This momentary blocking by diode 26prevents immediate reaction of the counter 21 from reaching the anode 2.

Specific component values for one particular circuit, as shown in Figure5, found satisfactory for amplifying radiation counter tube pulses aregiven below:

Potential of source 2| volts-- 900-950 Radiation counter tube resistance22 megohms 2 Input capacitor i0 mmf 100 Fixed anode resistor 24 megohms2 Variable `anode resistance I2 do 2 4 Output capacitor I5 mmf 100 Loadresistor 26 ohms 100,000

Rectifiers I6 and 26 are germanium crystal diodes.

Maximum pulse amplifying rate is 1000 counts per sec.

From the above description it will be apparent that there is thusprovided a device of the character described possessing the particularfeatures of advantage before enumerated as desirable, but whichobviously is susceptible of modification in its form, proportions,detail construction and arrangement of parts Without departing from theprinciple involved or sacricing any of its advantages.

While in order to comply with the statute, the

'l invention has been described in language more or less specic as tostructural features, it is to be understood that the invention is notlimited to the specific features shown, but that the means andconstruction herein disclosed comprise a preferred form of putting theinvention into effect, and the invention is, therefore, claimed in anyof its forms or modications within the legitimate and valid scope of theappended claims.

What is claimed is:

1. A pulse amplifier comprising a tube having an envelope containing ananode, a cold cathode, a cold trigger electrode and a filling ofionizable gas at glow discharge pressure providing a negativevoltage-current curve slope, a source 0f potential greater than thefiring voltage of said tube, connected across said anode and saidcathode, resistance means in series with said source and said anode toadjust said tube to glow stably between said anode and said cathodeclose to an unstable condition on the negative slope of said curve,input means for applying a negative pulse to said trigger electrode toextinguish said glow, said glow being re-established automatically dueto voltage rise through said resistance means, a capacitor and diodeseries combination connected in shunt across said anode and said cathodeproviding a means of storage of energy from said source duringextinction time oi said glow, and an output line connected across saiddiode and said cathode to emit a negative pulse generated by said glowre-establishment.

2. A pulse amplifier comprising a tube having an envelope containing ananode, a cold trigger electrode, a cold control cathode and a filling ofionizable gas at glow discharge pressure providing a negativevoltage-current curve slope, a source of potential greater than thefiring voltage of said tube, connected across said anode and saidworking cathode, resistance means in series with said source and saidanode to adjust said tube to glow stably between said anode and saidcathode close to an unstable condition on the negative slope or saidcurve, input means for applying a negative pulse to said triggerelectrode to extinguish said glow, said glow being re-establishedautomatically due to voltage rise through said resistance means, and anoutput line connected across said anode and said cathode to receive apositive pulse generated by said glow interruption, and means in saidoutput line for inverting said positive pulse to a negative outputpulse, said latter means including a capacity in series with arectifying diode across said anode and cathode.

3. A pulse amplier in accordance with claim 1 wherein a radiationcounter tube forms a part of said input means and wherein a multi-stagepulse counter is connected to said output line through a rectifyingdiode oriented to prevent reection of energy toward said tube.

4. A pulse amplier in accordance with claim 1 wherein a radiationcounter tube forms a part of said input means and wherein a multi-stagepulse counter is connected to said output line through a rectifyingdiode oriented to prevent reflection of energy toward said tube, and ashunt resistor across the input of said counter.

CHARLES R. WILLIAMS. GLENN E. HAGEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,950,003 Hund Mar. 6, 19341,951,416 Hund Mar. 20, 1934

